Mild cosmetic compositions must satisfy a number of criteria including cleansing power, foaming properties and mildness/low irritancy/good feel with respect to the skin, hair and the ocular mucosae. Skin is made up of several layers of cells which coat and protect the keratin and collagen fibrous proteins that form the skeleton of its structure. The outermost of these layers, referred to as the stratum corneum, is known to be composed of 250 .ANG. protein bundles surrounded by 80 .ANG. thick layers. Hair similarly has a protective outer coating enclosing the hair fibre which is called the cuticle. Anionic surfactants can penetrate the stratum corneum membrane and the cuticle and, by delipidization destroy membrane integrity. This interference with skin and hair protective membranes can lead to a rough skin feel and eye irritation and may eventually permit the surfactant to interact with the keratin and hair proteins creating irritation and loss of barrier and water retention functions.
Ideal cosmetic cleansers should cleanse the skin or hair gently, without defatting and/or drying the hair and skin and without irritating the ocular mucosae or leaving skin taut after frequent use. Most lathering soaps, shower and bath products, shampoos and bars fail in this respect.
Certain synthetic surfactants are known to be mild. However, a major drawback of most mild synthetic surfactant systems when formulated for shampooing or personal cleansing is poor lather performance compared to the highest shampoo and bar soap standards. Thus, surfactants that are among the mildest, such as sodium lauryl glyceryl ether sulfonate, (AGS), are marginal in lather. The use of known high sudsing anionic surfactants with lather boosters, on the other hand, can yield acceptable lather volume and quality but at the expense of clinical skin mildness. These two facts make the surfactant selection, the lather and mildness benefit formulation process a delicate balancing act.
Despite the many years of research that have been expended by the toiletries industry on personal cleansing, the broad mass of consumers remain dissatisfied by the mildness of present day cleansing compositions, finding, for example, that they have to apply a separate cosmetic lotion or cream moisturizer to the skin after using a shower or bath preparation in order to maintain skin suppleness and hydration and to counteract the delipidizing effect of the cleanser.
It is known from the art that inclusion of oils in bathing compositions can provide post-use skin feel benefits. However incorporation of oils at levels sufficient to deliver consumer noticeable benefits has until now proved to be a challenge, particularly with respect to the delivery of good, stable lather characteristics in the presence of oil and avoiding unpleasant `slimy`/`greasy` water feel or oily appearance during use while still delivering a desirable after-use soft skin feel. A further difficulty associated with combining high levels of oil with conventional detergent systems has been the achievement of a stable system in which the oil is deposited onto the skin in a non-greasy manner during use. It has now been found that personal cleansing compositions having excellent skin feel attributes both for in use feel and after use feel as well as good lather volume, stability and feel characteristics in combination with improved product stability can be provided by the use of particular polyol polyester oil components. It has also been found that combination of oil components having particular oil/surfactant solution interfacial tension characteristics are especially valuable for the provision of product stability and skin deposition characteristics.
Thus a need exists for personal cleansing products which will not dehydrate the skin or result in loss of skin suppleness, which will provide a level of skin conditioning and emolliency performance which previously has only been provided by a separate post-cleansing cosmetic moisturizer and which will produce a foam which is stable and of high quality both in lather volume and appearance, which are effective hair and skin cleansers, which have good in-use aesthetics, rinsibility characteristics, and which at the same time have stable product and viscosity characteristics and remain fully stable under long term and stressed temperature storage conditions.